The general objective of this project is to elucidate the mechanisms by which the interaction of actin and myosin underlying contraction of vascular smooth muscle is regulated. The specific objectives of this proposal are to determine: 1. the relation between myosin light chain phosphorylation and force development, and 2. he factors that contribute to the control of phosphorylation-dephosphorylation system and the actin-activated ATPase activity of vascular smooth muscle myosin.